Biology subjects

Deol, K. K.

Publications and source records attributed to Deol, K. K..

9 recordsLinked to original sources

bioRxiv2025

Induced ubiquitination bypasses canonical ERAD to drive ER protein degradation

Heterobifunctional proteolysis-targeting chimeras (PROTACs) have emerged as a powerful strategy to degrade disease-relevant proteins, enabling targeting of previously "undruggable" proteins. Current degrader molecules primarily target cytosolic substrates, yet nearly one-third of the proteome resides in or transits the endoplasmic reticulum (ER), including receptors, secreted factors, and biosynthetic enzymes with high therapeutic relevance. Whether ER-localized proteins can be broadly targeted for induced degradation remains an open question. To address this gap, we employed a panel of fluorescent reporter cell lines and used the dTAG chemical-genetic system to recruit cytosolic E3 ligases. While lumenal substrates segregated from the cytosol were resistant to degradation, recruitment of cytosolic ligases effectively degraded ER membrane proteins across multiple topologies and with post-translational modifications. CRISPR genetic screens revealed that the induced degradation required the expected cullin RING ligase complexes but surprisingly bypassed ER-associated degradation (ERAD) machinery, with the exception of the AAA ATPase VCP. Mechanistic studies demonstrated that substrate ubiquitination was essential for VCP binding, and cleavage of ubiquitin chains released VCP, suggesting a model in which VCP directly extracts substrates independent of a dislocation apparatus. Extending this strategy to an endogenous substrate, we synthesized an HMGCR ERAD-TAC by linking atorvastatin to a cereblon E3 ligase recruiter and found that HMGCR degradation was likewise VCP-dependent. Together, these findings demonstrate that ER membrane proteins are generally susceptible to induced degradation via cytosolic ligase recruitment, uncovering a VCP-centered mechanism that operates independently of membrane-embedded ERAD machinery. This work establishes foundational principles for extending targeted protein degradation to the early secretory pathway. SIGNIFICANCE STATEMENTTargeted protein degradation has transformed drug discovery. Nearly one-third of the proteome reside in or transit the endoplasmic reticulum (ER), a compartment rich in therapeutically relevant but structurally complex targets. Whether these ER proteins can be broadly degraded using PROTACs has remained unknown. Here, we define the minimal requirements for degrading ER membrane proteins by recruiting cytosolic E3 ligases. Using chemical-genetic tools, genetic screens, and a statin-based degrader, we show that ubiquitination engages the VCP extraction machinery, enabling degradation of diverse ER membrane proteins independent of canonical ER-associated degradation components. These findings reveal a ubiquitin-driven route for membrane protein turnover, expand the landscape of druggable ER proteins, and establish principles for designing degraders operating in the early secretory pathway.

cell biology↗

bioRxiv2025

Vitamin B2 metabolism promotes FSP1 stability to prevent ferroptosis

Ferroptosis, a regulated form of cell death driven by excessive lipid peroxidation, has emerged as a promising therapeutic target in cancer. Ferroptosis suppressor protein 1 (FSP1) is a critical regulator of ferroptosis resistance, yet the mechanisms controlling its expression and stability remain mostly unexplored. To uncover regulators of FSP1 abundance, we conducted CRISPR-Cas9 screens utilizing a genome-edited, dual-fluorescent FSP1 reporter cell line, identifying both transcriptional and post-translational mechanisms that determine FSP1 levels. Notably, we identified riboflavin kinase (RFK) and FAD synthase (FLAD1), enzymes which are essential for synthesizing flavin adenine dinucleotide (FAD) from vitamin B2, as key contributors to FSP1 stability. Biochemical and cellular analyses revealed that FAD binding is critical for FSP1 activity. FAD deficiency, and mutations blocking FSP1-FAD binding, triggered FSP1 degradation via a ubiquitin-proteasome pathway that involves the E3 ligase RNF8. Unlike other vitamins that inhibit ferroptosis by scavenging radicals, vitamin B2 supports ferroptosis resistance through FAD cofactor binding, ensuring proper FSP1 stability and function. This study provides a rich resource detailing mechanisms that regulate FSP1 abundance and highlights a novel connection between vitamin B2 metabolism and ferroptosis resistance with implications for therapeutic strategies targeting FSP1 in cancer.

cell biology↗

bioRxiv2024

CLCC1 promotes hepatic neutral lipid flux and nuclear pore complex assembly

Imbalances in lipid storage and secretion lead to the accumulation of hepatocyte lipid droplets (LDs) (i.e., hepatic steatosis). Our understanding of the mechanisms that govern the channeling of hepatocyte neutral lipids towards cytosolic LDs or secreted lipoproteins remains incomplete. Here, we performed a series of CRISPR-Cas9 screens under different metabolic states to uncover mechanisms of hepatic neutral lipid flux. Clustering of chemical-genetic interactions identified CLIC-like chloride channel 1 (CLCC1) as a critical regulator of neutral lipid storage and secretion. Loss of CLCC1 resulted in the buildup of large LDs in hepatoma cells and knockout in mice caused liver steatosis. Remarkably, the LDs are in the lumen of the ER and exhibit properties of lipoproteins, indicating a profound shift in neutral lipid flux. Finally, remote homology searches identified a domain in CLCC1 that is homologous to yeast Brl1p and Brr6p, factors that promote the fusion of the inner and outer nuclear envelopes during nuclear pore complex assembly. Loss of CLCC1 lead to extensive nuclear membrane herniations, consistent with impaired nuclear pore complex assembly. Thus, we identify CLCC1 as the human Brl1p/Brr6p homolog and propose that CLCC1-mediated membrane remodeling promotes hepatic neutral lipid flux and nuclear pore complex assembly.

cell biology↗

bioRxiv2023

Small molecule correctors divert CFTR-F508del from ERAD by stabilizing sequential folding states

Over 80% of people with cystic fibrosis (CF) carry the F508del mutation in the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride ion channel at the apical plasma membrane (PM) of epithelial cells. F508del impairs CFTR folding causing it to be destroyed by endoplasmic reticulum associated degradation (ERAD). Small molecule correctors, which act as pharmacological chaperones to divert CFTR-F508del from ERAD, are the primary strategy for treating CF, yet corrector development continues with only a rudimentary understanding of how ERAD targets CFTR-F508del. We conducted genome-wide CRISPR/Cas9 knockout screens to systematically identify the molecular machinery that underlies CFTR-F508del ERAD. Although the ER-resident ubiquitin ligase, RNF5 was the top E3 hit, knocking out RNF5 only modestly reduced CFTR-F508del degradation. Sublibrary screens in an RNF5 knockout background identified RNF185 as a redundant ligase, demonstrating that CFTR-F508del ERAD is highly buffered. Gene-drug interaction experiments demonstrated that correctors tezacaftor (VX-661) and elexacaftor (VX-445) stabilize sequential, RNF5-resistant folding states. We propose that binding of correctors to nascent CFTR-F508del alters its folding landscape by stabilizing folding states that are not substrates for RNF5-mediated ubiquitylation. SIGNIFICANCE STATEMENTO_LIClinically effective small molecule cystic fibrosis (CF) correctors divert mutant CFTR molecules from ER-associated degradation (ERAD). However, the mechanisms underlying CFTR ERAD are not well-understood. C_LIO_LIThe authors used CRISPR knockout screens to identify ERAD machinery targeting CFTR-F508del and found that the pathway is highly buffered, with RNF185 serving as a redundant ubiquitin ligase for RNF5. Gene-drug interaction experiments demonstrated that correctors act synergistically by stabilizing sequential RNF5-resistant folding states. C_LIO_LIInhibiting proteostasis machinery is a complementary approach for enhancing current CF corrector therapies. C_LI

cell biology↗

bioRxiv2022

A genome-wide CRISPR screen implicates plasma membrane asymmetry in exogenous C6-ceramide toxicity

The bioactive sphingolipid ceramide impacts diverse cellular processes (e.g., apoptosis and cell proliferation) through its effects on membrane dynamics and intracellular signalling pathways. The dysregulation of ceramide metabolism has been implicated in cancer evasion of apoptosis and targeting ceramide metabolism has potential therapeutic benefits as a strategy to kill cancer cells and slow tumor growth. However, the mechanisms of cancer cell resistance to ceramide-mediated cell death are vastly intertwined and incompletely understood. To shed light on this mystery, we performed a genome wide CRISPR-Cas9 screen to systematically identify regulators of cancer resistance to the soluble short chain ceramide, C6 ceramide (C6-Cer). Our results reveal a complex landscape of genetic modifiers of C6-Cer toxicity, including genes associated with ceramide and sphingolipid metabolism, vesicular trafficking, and membrane biology. Furthermore, we find that loss of the phospholipid flippase subunit TMEM30A impairs the plasma membrane trafficking of its binding partner the P4-type ATPase ATP11B, and depletion of TMEM30A or ATP11B disrupts plasma membrane asymmetry and promotes resistance to C6-Cer toxicity independent of alterations in C6-Cer uptake. Together, our findings provide a resource of genetic modifiers of C6-Cer toxicity and reveal an unexpected role of plasma membrane asymmetry in C6-Cer induced cell death.

cell biology↗

bioRxiv2022

Parallel CRISPR-Cas9 screens reveal mechanisms of PLIN2 and lipid droplet regulation

Lipid droplets (LDs) are lipid storage organelles that consist of a central core of neutral lipids surrounded by a phospholipid monolayer decorated with a unique set of integral and peripheral proteins. Invariably, at least one member of the perilipin family of proteins (PLIN1-5) associates with LDs in all cell types. Despite key roles of PLIN2 in governing hepatic lipid metabolism, the mechanisms that regulate PLIN2 levels remain incompletely understood. Here, we develop a set of genome-edited PLIN2 reporter cell lines that facilitate the analysis of genes that regulate PLIN2 and LD abundance. Leveraging these reporter cells in a series of CRISPR-Cas9 loss-of-function screens, we generate a comprehensive inventory of genes that influence PLIN2 levels under different metabolic conditions. Moreover, we uncouple their effects on PLIN2 expression and post-translational stability. Identified genetic modifiers include canonical genes that control LD metabolism (e.g., ACSL3, DGAT2, PNPLA2, ABHD5) as well as genes with less characterized roles in PLIN2 and LD regulation such as ubiquitination machinery (e.g., MARCH6, UBE2J2), transcription regulators (e.g., HNF4A, HDAC3), mitochondrial pathways (e.g., electron transport chain and mitochondrial fatty acid synthesis), and others. These CRISPR screens, and several published screens that focus on different aspects of lipid metabolism, provide the foundation for CRISPRlipid (http://crisprlipid.org), a versatile, online data commons for lipid-related functional genomics data. Together, our study uncovers new mechanisms of PLIN2 regulation and provides an extensive, phenotype-rich resource for the exploration of LD biology and lipid metabolism.

cell biology↗

bioRxiv2022

Ribosome stalling during selenoprotein translation exposes a ferroptosis vulnerability in cancer

Ferroptosis is a regulated, iron-dependent form of necrosis that is triggered by the accumulation of oxidatively damaged phospholipids1-3. Glutathione peroxidase 4 (GPX4) prevents ferroptosis by converting phospholipid hydroperoxides into non-toxic lipid alcohols4, 5. Ferroptosis has been implicated in the pathology of several degenerative conditions and inhibiting GPX4 activity has emerged as a therapeutic strategy to induce cancer cell death1, 2. However, many cancer cell lines are resistant to GPX4 inhibition6, and the mechanisms that regulate GPX4 activity and ferroptosis resistance remain incompletely understood. Here, employing a synthetic lethal CRISPR-Cas9 screen in a triple negative breast cancer (TNBC) cell line, we identify LRP8 (also known as ApoER2) as a ferroptosis resistance factor. LRP8 is upregulated in cancer, and we find that it promotes ferroptosis resistance in cancer cells in both 2-dimensional (2-D) cell culture and 3-dimensional (3-D) spheroid models. Mechanistically, loss of LRP8 decreases cellular selenium levels, resulting in the reduced expression of a subset of selenoproteins, including GPX4. Remarkably, the reduction in GPX4 is not due to the classic hierarchical selenoprotein regulatory program7, 8. Instead, our findings demonstrate that the translation of GPX4 is severely impaired in the selenium-deficient LRP8 knockout (KO) cells due to extensive ribosome stalling at the inefficiently decoded GPX4 selenocysteine (SEC) UGA codon, which results in ribosome collisions and early translation termination. Thus, our findings reveal ribosome stalling and collisions during GPX4 translation as targetable ferroptosis vulnerabilities in cancer cells.

cancer biology↗

bioRxiv2021

A Cryptic K48 Ubiquitin Chain Binding Site on UCH37 is Required for its Role in Proteasomal Degradation

Degradation by the 26S proteasome is an intricately regulated process fine-tuned by the precise nature of ubiquitin modifications attached to a protein substrate. By debranching ubiquitin chains composed of K48 linkages, the proteasome-associated ubiquitin C-terminal hydrolase UCHL5/UCH37 serves as a positive regulator of protein degradation. How UCH37 achieves specificity for K48 chains is unclear. Here, we use a combination of hydrogen-deuterium mass spectrometry, chemical crosslinking, small-angle X-ray scattering, NMR, molecular docking, and targeted mutagenesis to uncover a cryptic K48 ubiquitin chain specific binding site on the opposite face of UCH37 relative to the canonical S1 ubiquitin-binding site. Biochemical assays demonstrate the K48 chain-specific binding site is required for chain debranching and proteasome-mediated degradation of proteins modified with branched chains. Using quantitative proteomics, translation shutoff experiments, and linkage-specific affinity tools, we then identify specific proteins whose degradation depends on the debranching activity of UCH37. Our findings suggest that UCH37 and potentially other DUBs could use more than one S1 site to perform different biochemical functions.

biochemistry↗

bioRxiv2020

Proteasome-Bound UCH37 Debranches Ubiquitin Chains to Promote Degradation

The linkage, length, and architecture of ubiquitin (Ub) chains are all important variables in providing tight control over many biological paradigms. There are clear roles for branched architectures in regulating proteasome-mediated degradation, however the proteins that selectively recognize and process these atypical chains are unknown. Here, using synthetic and enzyme-derived ubiquitin chains along with intact mass spectrometry, we report that UCH37/UCHL5, a proteasome-associated deubiquitinase, exclusively cleaves K48 branched chains. The activity and selectivity toward branched chains is markedly enhanced by the proteasomal Ub receptor RPN13/ADRM1. Using proteasome complexes reconstituted with either active or inactive UCH37 together with protein substrates modified with branched chains, we find that chain debranching promotes degradation under multi-turnover conditions. These results are further supported by proteome-wide pulse-chase experiments, which show that the loss of UCH37 activity impairs global protein turnover. Our work therefore defines UCH37 as a debranching deubiquitinase important for promoting proteasomal degradation.

biochemistry↗